The invention relates to a damping device for absorbing structure-borne sound, the device comprising a wave conducting element with a succession of layers made of mass-spring elements and extending in the direction of the propagation of the waves.
An oscillation absorber of this generic type is described in German patent document DE 31 13 268 C2. In this absorber, the individual mass elements taper in the direction of the propagation of the structure-borne sound waves, so that the entire absorber has the shape of a part of a horn. The spring elements can either be made with elastic plastic materials or, in accordance with a particular exemplary embodiment of German patent document DE 31 13 268 C2, by means of spheres inserted into pan-shaped depressions of the mass elements. However, in either case the mass elements are rigid. While the employment of plastic materials is limited because of the relatively narrow temperature range, the use of spheres and corresponding pan-shaped depressions requires a relatively large outlay in fabrication.
It is therefore an object of the present invention to provide a broad-band vibration damping element in the form of a wave conductor, which can be produced with a small manufacturing outlay and, if possible, has no plastic material, or only a minute and easily detachable plastic portion.
This object is attained by the vibration damping element according to the invention which has a succession of layers of mass-spring elements, the layers being arranged in the direction of propagation of the mechanical waves. The mass-spring elements are formed as bending beams or plates having a decreasing resilience in the wave propagation direction and are connected with each other in a frictional or torque-activated manner with intervening spaces which are offset relative to each other, so that when a force is applied normal to their surface, at least one mass-spring element is bent.
In contrast to the prior art, there is no separate spring element in the segmented wave conductor of the oscillation absorber in accordance with the invention. Instead, the required resilience is provided by the natural elastic properties of the mass elements. This is achieved by providing the mass elements in the form of flexible beams or plates which bend under oscillation-caused pressure or pull. Combined mass-spring elements are thus created.
The function of the flexible beams or plates is achieved in a particularly simple manner by providing the individual mass-spring elements with spacers, with at least one spacer of a mass-spring element being arranged between two spacers of the adjoining mass-spring element. Since the transfer of force takes place via the spacers, each spacer presses approximately against the center of the area of a mass-spring element which is supported between two spacers or the adjacent mass-spring element. Each mass-spring element is thus bent transversely to the direction of wave propagation.
The spring elements can also be made by notching or tapering a mass element to form flexible areas therein, each having a spacer disposed thereon.
A particularly simple way of creating a spacer between two mass-spring elements is by spot welding. So that there is sufficient spacing between the mass-spring elements, the welding spot should suitably be placed on a slight elevation created, for example, by stamping.
If the internal friction in the bending mass-spring elements should not be sufficient to fully damp the vibration, the wave conducting element can be provided with a reflection-free end, as disclosed in German Patent Publication DE 31 13 268 C2. To increase damping, it is also possible to surround the exterior wall areas of the wave conducting element (that is, the stack of mass-spring elements placed on top of each other in layers, connected by spacers) with a damping material. If required, this can then easily be removed again or replaced.
If the vibration absorber is intended to be effective in all three translatory and three rotational degrees of freedom, it is advantageous to dispose an additional spring and/or a damping material between the mass-spring elements.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.